The delivery of radio frequency (RF) energy to target regions within solid tissue is known for a variety of purposes of particular interest to the present invention. In one particular application, RF energy may be delivered to diseased regions (e.g., tumors) for the purpose of ablating predictable volumes of tissue with minimal patient trauma.
RF ablation of tumors is currently performed using one of two core technologies. The first technology uses a single needle electrode, which when attached to a RF generator, emits RF energy from an exposed, uninsulated portion of the electrode. The second technology utilizes multiple needle electrodes, which have been designed for the treatment and necrosis of tumors in the liver and other solid tissues. U.S. Pat. No. 6,379,353 discloses such a probe, referred to as a LeVeen Needle Electrode™, which comprises a cannula and an electrode deployment member reciprocatably mounted within the delivery cannula to alternately deploy an electrode array from the cannula and retract the electrode array within the cannula. Using either of the two technologies, the energy that is conveyed from the electrode(s) translates into ion agitation, which is converted into heat and induces cellular death via coagulation necrosis. The ablation probes of both technologies are typically designed to be percutaneously introduced into a patient in order to ablate the target tissue.
In the design of such ablation probes, which may be applicable to either of the two technologies, RF energy is often delivered to an electrode located on a distal end of the probe's shaft via the shaft itself. This delivery of RF energy requires the probe to be electrically insulated to prevent undesirable ablation of healthy tissue. In the case of a single needle electrode, all but the distal tip of the electrode is coated with electrically insulative material in order to focus the RF energy at the target tissue located adjacent the distal tip of the probe. In the case of a LeVeen Needle Electrode™, RF energy is conveyed to the needle electrodes through the inner electrode deployment member, and the outer cannula is coated with an electrically insulative material to prevent RF energy from being transversely conveyed from the inner electrode deployment member along the length of the probe.
RF energy is commonly delivered to the electrode element of a tissue ablation probe (whether a single needle electrode or needle electrode array, deployable or otherwise) and thus to tissue in one of several ways. In one arrangement, RF current is delivered to an ablation electrode element in a monopolar fashion, wherein current passes from the ablation electrode element to a dispersive electrode attached externally to the patient, such as a contact pad placed on the patient's flank. In another arrangement, the RF current is delivered to two electrodes in a bipolar fashion, wherein current passes between “positive” and “negative” electrodes in close proximity to each other, e.g., two electrodes on the same probe or array or on different probes or arrays. Bipolar arrangements require the RF energy to traverse through a relatively small amount of tissue between the tightly spaced electrodes and are generally more efficient than monopolar arrangements, which require the RF energy to traverse through the thickness of the patient's body. Thus, bipolar ablation probes generally create larger and/or more efficient lesions than monopolar ablation probes. Additionally, bipolar arrangements are generally safer for the physician and patient, since the monopolar arrangement presents the risk that the physician and patient may become a ground in the monopolar arrangement, resulting in painful burns.
Currently, bipolar LeVeen-type ablation probes comprising two axially arranged deployable electrode arrays (a proximal electrode array and a distal electrode array) combine the advantages that accompany the use of electrode arrays and bipolar ablation. Details regarding the structure and operation of such bipolar ablation probes are disclosed in U.S. Patent Publication 2002/0022864, entitled “Multipolar Electrode System for Radiofrequency Ablation,” and U.S. patent application Ser. No. 09/663,048, entitled “Methods and Systems for Focused Bipolar Tissue Ablation,” both of which are expressly incorporated herein by reference.
In a typical tumor diagnostic and therapeutic procedure, tissue suspected of containing an abnormality is imaged using a high definition imaging modality, such as Magnetic Resonance Imaging (MRI). If an abnormality, such as a tumor, is discovered, a sample of the abnormal tissue may be retrieved by percutaneously introducing a biopsy needle through healthy tissue into contact with the abnormal tissue to obtain a tissue sample for laboratory analysis. The treating physician may further proceed with treating the tumor immediately after performing the biopsy, or after analysis of the malignancy indicates further treatment is needed.
In either case, the tumor can be treated by percutaneously introducing an RF ablation probe through the patient's body to contact the tumor in a similar manner as the biopsy needle described above. The ablation probe can then be operated to ablate the tumor, after which the ablated region can be treated with a therapeutic agent, such as a drug. This may be accomplished by introducing a separate drug delivery device into the ablated region in the same manner as the biopsy needle and ablation probe.
In performing the diagnostic/therapeutic procedure, the biopsy stylet, RF ablation probe, and drug delivery device can either be percutaneously introduced into the patient's body as stand-alone devices or as parts of a co-access delivery system. In the former case, each device may follow a different path than the devices before it, and thus must be meticulously delivered to the targeted region in the patent's body under an imaging modality, such as fluoroscopy and/or CT. The multiple tissue insertions also increase the pain and discomfort suffered by the patient during this procedure. When a co-access delivery system is used, however, each device is delivered through a single cannula that advantageously provides a more accurate delivery of the devices to the targeted region. That is, after the biopsy stylet has been delivered through the cannula and a biopsy is taken from the center of the targeted region, the cannula provides a convenient place marker for subsequent delivery of the ablation probe and drug delivery device to the targeted region without the need for navigational imaging. The use of a co-access delivery system also only requires a single percutaneous insertion, i.e., insertion of the cannula.
In some co-access system models, the cannula includes an axial opening on the distal end in addition to side slots through which one or more electrode arrays may deploy. However, the side slots typically remain in an open configuration. Thus, if a user wishes to deliver a substance, such as a pharmaceutical agent, through the open distal end of the cannula to a small, targeted tissue area, the substance may leak out of the side slots. This prevents accurate delivery of the pharmaceutical agent. Also, when it is desired to deliver a pharmaceutical agent to different regions of target tissue, the open slots and the open distal end cause difficulty in selecting and delivering the pharmaceutical agent to multiple select areas.
Therefore, there is a need in the art for a co-access ablation probe that allows multiple electrodes to be properly deployed, while also allowing for proper placement of other medical elements, within a treatment region of a patient.